Medical treatments using balloon dilation catheters, for example, Percutaneous Transluminal Angioplasty, have evolved to the point where such treatments require the insertion of catheters into narrower and more remote blood vessels within the body. This evolution has required the use of catheters having correspondingly smaller shaft diameters and longer shaft lengths. The migration toward catheters with smaller diameter longer shafts presents several challenges, not the least of which is catheter balloon inflation/deflation rates. As will be appreciated, as the diameter of catheter shafts has decreased the cross-sectional area available for inflation/deflation lumens has decreased. As the length of catheter shafts has increased, the pressure drop along the length of the inflation/deflation lumen or lumens has also increased. Hence, the amount of time required to inflate or deflate catheter balloons has increased as the diameter of catheter shafts has decreased and the lengths of such shafts has increased.
One conventional design for balloon dilation catheters is a coaxial design wherein two concentrically disposed tubular members form the catheter shaft. The bore of the inner tubular member forms the guidewire lumen with the outer tubular member forming the catheter shaft body. The annular space between the outer surface of the inner tubular member and the inner surface of the outer tubular member forms an inflation/deflation lumen for transporting an inflation medium such as a noncompressible fluid to inflate and deflate the dilation balloon. The inflation/deflation performance of a coaxial catheter is determined by the difference in cross-sectional area between the inside diameter of the outer tubular member and the outside diameter of the inner tubular member along with the length of the catheter shaft. For a given combination of catheter diameter and guidewire lumen diameter, the coaxial design is considered to maximize the cross-sectional area available for the inflation/deflation lumen thereby providing the best inflation/deflation performance for a given catheter length.
The balloon of a catheter utilizing the coaxial design is fastened at its proximal end to the distal end of the outer tubular member. The distal end of the balloon is fastened to the inner tubular member. However, the outer tubular member is not mechanically attached to the inner guidewire tubular member, rather the inner tubular member floats free within the outer tubular member. When inflated, the balloon may tend to elongate rather than expand in a radial direction since the distal end of the balloon is attached to the inner tubular member which may move longitudinally relative to the outer tubular member. The tendency to elongate detracts from the inflation performance of the balloon and additionally, places additional stresses on the joints where the proximal end of the balloon is attached to the outer tubular member and where the distal end of the balloon is attached to the guidewire tubular member.
Other conventional catheter designs utilize non-coaxial and separate guidewire and inflation lumens. These non-coaxial designs are referred to as “multi-lumen” catheters even though it is appreciated that coaxial designs have multiple lumens as well. In keeping with industry practices, for the purpose of this application, the term “multi-lumen” refers to designs wherein the guidewire lumen and inflation/deflation lumens are not coaxial. There are at least two types of multi-lumen catheter shafts: dual lumen shafts and extruded dual port shafts. In dual lumen shafts, a first tubular member forming the guidewire lumen therewithin and a second tubular member forming the inflation/deflation lumen therewithin run parallel to one another within a full diameter outer jacket surrounding both lumens. Since only the guidewire lumen member and the inflation/deflation lumen member (i.e., not the outer jacket) are exposed to the balloon inflation pressure, only these relatively small diameter tubular members need to be strong enough to withstand such pressures, and the full-diameter outer jacket of the catheter can be made of a softer and/or thinner material.
The other type of multi-lumen catheter, i.e., the extruded dual port shaft has guidewire and inflation/deflation lumens that are integrally formed longitudinal voids created during extrusion of the plastic or resin catheter shaft. The extrusion process enables construction of the catheter shaft and the lumens in non-circular geometries such as semi-circular or crescent. However, for the same diameter, or cross sectional area, the geometry of extruded dual port shafts and dual lumen shafts is inferior to the coaxial design in terms of inflation/deflation performance.
Hence, while multi-lumen shaft designs may present several advantages such as improved trackability, the cross-sectional configuration of such catheter shafts result in inflation/deflation performance that is inferior to that of coaxial shafts.
Thus, there exists a need for a balloon catheter having a shaft with inflation/deflation performance similar to that of a conventional coaxial design without the disadvantages thereof.